Upload
amable
View
56
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Upcoming Classes. Tuesday, Sept. 25 th Entropy and the Second Law Assignment due: * Read “Exploiting Heat”, The New Way Things Work, D. Macaulay, Pages 142-157 Thursday, Sept. 27 th First set of Oral Presentations Assignment due: * First term paper or oral presentation. - PowerPoint PPT Presentation
Citation preview
Upcoming ClassesTuesday, Sept. 25th
Entropy and the Second LawAssignment due:
* Read “Exploiting Heat”, The New Way Things Work, D. Macaulay, Pages 142-157
Thursday, Sept. 27th First set of Oral PresentationsAssignment due:
* First term paper or oral presentation
Upcoming ClassesThursday, Sept. 27th
First set of Oral PresentationsAssignment due:
* First term paper or oral presentation
Tuesday, Oct. 2nd Midterm ExamAssignment due:
* Study for the midterm
Upcoming Deadlines
Thursday, September 27th First Set of Oral PresentationsFirst term paper (if not giving presentation)
Thursday, October 11th
Outline of second oral presentation or written paper
Oral PresentationsThe following persons will give oral presentations
on Thursday, September 27th :• Batres, Adan• Boyd, Heidi• Chen, Emily• Kwiatkowski, Dajon• Lebedeff, Christopher• Lipton, ChristopherFor everyone else, your first term paper is due on
that date.
Oral Presentations (II)The following persons will give oral presentations
on Tuesday, November 6th :• Luttrell,Katherine• Macdonald,Keith• McDonald,Kathleen• Mendoza,Jazmin• Nguyen,Jennifer• Nguyen,LindaFor everyone else, term paper is due on that date.
Midterm ExamMidterm exam will consist of four short essay questions.Material up to and including: “Energy and the First Law” lecture; “The
Mechanics of Movement” reading.Closed book but allowed one page of notes (front & back).Sample questions:
“List three ways that a painter can create a sense of distance in a painting. Describe one of the ways in detail.”“What is a fractal? Give two examples of fractals and an example of something that is not a fractal.” “Explain the physics of balance. Give examples related to dance.”
Midterm counts for one homework assignment.
Extra Credit: SF Museum of Art
Visit San Francisco Museum of Modern Art and see Abstract Expressionist paintings.
Turn in your ticket receipt ($7 for students). Worth one homework assignment; deadline is Oct. 16th
Guardians of the Secret, Jackson Pollock, 1943
Extra Credit: San Jose Ballet
See a performance of San Jose Ballet in San Jose Center for Performing Arts (Nov. 15th – 18th ).
Turn in your ticket receipt. Worth one homework assignment or three quiz/participation credits.
Ramon Moreno in CARMINA BURANA
Extra Credit: Cypress QuartetSJSU Celebrates 150th with Cypress String
Quartet Event Fusing Precision Playing with World-Class Technology
SJSU Music Concert Hall, 7 p.m. Thur., Sept. 20th.I will hand out tickets at the door from 6:30 to 6:50pm; don’t be late to the performance! Worth two quiz/participation extra credits.
TONIGHT!
David Chai, AnimatorYour flip-book homework was judged by David Chai
of Thunderbean Animation Studios and San Jose State University.
Energy & The First Law
DesignDesign is often a blending of art & scienceArchitecture
FashionDesign
Product Design &Graphic Design
Physics of Drapery
Artist’s drawing(A. Durer, 1500) Vera Wang
Wedding Dress (2006)
Elements of Draping Proceedings of the National Academy of Sciences (2004)
Drapery is a surprisingly difficult physics problem
Frank Gehry, ArchitectModern engineering and science tell us that the designs of Frank Gehry can be built and are safe.
Fundamental question in design: What are the limitations placed by the laws of physics?
Hotel in Spain
MIT, BostonDisney Concert Hall, Los Angeles
Fundamental Design QuestionsCan you design a machine that creates a
large force using a small force?Can you design a machine that creates a
lot of energy using a little energy?
Burj Dubai
Hybrid car
Kinetic Energy (KE)
Kinetic energy is energy of motion.
Kinetic energy of an object is,
(Kinetic Energy) = ½ x (Mass) x (Speed)2
A stationary object has zero kinetic energy.
Supertanker and bullet both have large kinetic energies
Potential Energy (PE)
Gravitational potential energy of an object is,
(Potential Energy) = (Weight) x (Height)
Think of potential energy as stored energy or energy “in the bank.”
Metric unit of energy is Joules.
10 m
PE = 600 J, KE = 600 J
The First Law20
m
6 kgPE = 1200 J, KE = 0 J
PE = 0 J, KE = 1200 J
Energy is the “currency” of motion
Can calculate the kinetic and potential energy of a falling bowling ball
Ramp
RollerCoaster
Conservation of Energy
Conservation of mechanical energy is
(Potential Energy) + (Kinetic Energy)
stays constant during motion.
Energy “bookkeeping” makes motion simple.
Types of Energy
In this lecture we’ll consider mechanical energy but there’s also:
• Thermal energy• Chemical energy• Electrical energy• Solar energy*• Nuclear energyTotal energy is conserved, once we account for
the various different forms it can transform into.* Actually a form of electrical energy
Demo: Ball Races
Ball on track B has less potential, thus more kinetic energy (and greater speed) during most of the race.
Which ball wins the race, A or B?
Energy and Force
To stop an object with a large kinetic energy requires either:
• Large force (stopping the object quickly).• Small force applied for a long distance.
Notice that changing object’s energy depends on force and distance.
Demo: Egg Throw
Throw a raw egg as fast as possible at a plastic sheet that’s held loosely.
X X
X
X
X (Hold here)
Demo: Vampire Stake
Place a heavy stake on my chest and strike with a hammer. Why am I not killed?
(force) x (DISTANCE)
X XOuch!
(FORCE) x (distance)
Not safe if stake strikes hard skull
Soft, fleshychest
Automobile SafetyMaximizing the distance during impact on the driver
minimizes the force of impact. Used in design of:
Seatbelts Air Bags CrumpleZones
Work
Define work done on an object by a force as
(Work) = (Force) X (Distance traveled)
Force acting in direction of motion: Positive work.Force acting in opposite direction: Negative work.Force perpendicular to motion: Zero work
Change in energy equals the work done on by forces
Check YourselfSlaves pull a heavy load.Work done by slaves is
positive, negative, or zero?Positive work.Work done by friction force?Negative work.Work done by the ground?Zero. Support does no work.
LOAD
SupportPull
Friction
Ramp (Inclined Plane)Ramps allow us to lift a heavy object using a
small force by pushing over long distance.
(BIG FORCE) X (short distance)
(small force) X (LONG DISTANCE)
Two persons do the same work but exert different forces.
PyramidsRamps allowed ancient civilizations to lift enormous stones to build pyramids
KnifeKnife is a wedge that exerts a large force
over a small distance by exerting a small force over a large distance.
Push down large distance with small force
Wedge exerts large force for a small distance
Zipper
The zipper, patented in 1917, has interlocking teeth separated or joined by a wedge.
Wedge
Gideon Sundback’s patent for the "Separable Fastener"
Lever
Lever also converts a small force into a large force by ratio of distances acting.
Push down with a small force over a large distance
Lift a large weight over a small distance
First Class Levers
Fulcrum is located in between the input force (effort) and the output force (load)
Fulcrum
Effort ArmLoadArm
(Load force)/(Effort force) = (Effort Arm)/(Load Arm)
Second & Third Class Levers
Third Class Lever(Load, Effort, Fulcrum)
Second Class Lever(Effort, Load, Fulcrum)
Effort Arm
LoadArm
Effort Arm
LoadArm
Examples of LeversCrowbar
Wheel barrow
Scissors
Trebuchet
EffortLoad
Fulcrum
Human Arm as a Lever
Bicep muscle exerts an effort force close to your elbow (fulcrum) to raise your forearm (load).
This is a third class lever so a large effort force acts over a small distance to move a small load over a large distance.
Cantilever
Cantilevers are used in architecture to support hanging beams and platforms
CantileverEffort
LoadFulcrum
Fallingwater house (1935)designed by Frank Lloyd Wright
SupportWeight
Piano KeyA piano key a simple
lever that when pressed down by a pianist, pushes up against another lever, the whippen.
Whippen
Effort
Load Fulcrum
Whippen LeverAs the capstan pushes up
the whippen, which then pushes the jack upwards against the hammer while pushing the spoon towards the damper.
whippen
jack
capstanEffort
Load
Jack & Hammer
Jack rises, pushes the hammer towards the string, then is pulled away from the hammer when it hits the letoff button. Hammer swings and hits the string.
JackJack
Hammer
Effort
Load
Effort
Load
Demo: Hanging Hammer
Oddly, the hinge doesn’t open when the hammer hangs from the board. Why?
Center ofGravity
If the hinge opened then the center of gravity, located near the hammer’s head, would rise. This would be a spontaneous increase in the potential energy of an object at rest. That’s impossible, in the same way that a ball won’t spontaneously roll uphill.
Hinge
Perpetual Motion Machines
Is it possible to design a machine that runs forever, creating its own source of energy?
No. By the First Law, energy may be transferred from one form to another but it may neither be created nor destroyed.
Perpetual motion machines are impossible, but that’s not stopped people from trying.
Overbalanced WheelLeonardo da Vinci’s notebooks show his analysis of perpetual motion ideas that originated in 8th century India and reached Europe via Arabia
Wheel seems to perpetually turn due to imbalance between left and right sides
Perpetual Motion & LeversOverbalanced wheel may
appear as if could start from rest, begin turning and continue to turn clockwise forever.
Does not turn at all because the weights on the left have a shorter effort arm than the load arm on the right.
Effort
Load
Effort ArmLoadArm
You might set yourself to prove that by equipping such a wheel with many balances, … the wheel would stand in perpetual movement. But by this you would be deceiving yourself.
Leonardo da Vinci
Perpetual Motion & Ramps
Will the chain of balls rotate clockwise or counter-clockwise?
Neither since the energy gained going up one side of the ramp exactly equals the energy lost going down the other side.
U.S. Patent OfficeFrom General Information Concerning Patents:“A working model, or other physical exhibit, may
be required by the Office if deemed necessary. This is not done very often. A working model may be requested in the case of applications for patent for alleged perpetual motion devices.”
"It may be perpetual motion, but it will take forever to test it."
Cartoon by Donald Simanek.
Next Lecture Entropy & the Second Law
Remember:Assignment due:
Read “Exploiting Heat”, The New Way Things Work, D. Macaulay, Pages 142-157